1. Field of Invention
The invention relates to an in-cylinder injection type spark-ignition internal combustion engine in which a fuel directly injected into a cylinder is combusted using a spark plug. In particular, the invention relates to stabilizing the combustion when the engine is cold-started.
2. Description of Related Art
In recent years, an in-cylinder injection type gasoline engine that has realized lean burning has become widely used. Japanese Patent Laid-Open Publication No. 11-324778 describes an example of such technology. The technology described in the publication is configured so that an intake valve opens when the crank angle has passed a predetermined angle after the exhaust valve is closed to prevent concurrent oil dilution and smoking at the time of cold starting. Furthermore, the technology described in the publication is designed so that a fuel is injected while both valves are closed. As mentioned above, the technology described in the publication prevents the time period where the exhaust valve opens and the time period where the intake valve opens from being overlapped. Accordingly, a part of high temperature combustion gas is allowed to remain in the combustion chamber. Moreover, a fuel is injected into the combustion chamber in which a part of the high temperature combustion gas remains, and thus the fuel atomization is accelerated. It is mentioned in the publication that the above configuration can inhibit fuel from being adhered to a piston crown surface or to a cylinder bore wall surface, and thus it can inhibit both the smoking and oil dilution.
However in the above mentioned technology, fuel is injected at an early timing of the intake stroke when the engine is cold-started. Thus, homogeneous air-fuel mixture is essentially formed to cause stratified charge combustion. Therefore, the technology cannot realize a lean burning using a stratified charge combustion, and accordingly decreases fuel efficiency.